Exhaust aftertreatment burner with preheated combustion air

ABSTRACT

A burner for an exhaust aftertreatment system may include a housing assembly and an ignition device. The housing assembly may include an inner shell surrounded by intermediate and outer shells. The inner shell may at least partially define a combustion chamber. The housing assembly may include an airflow passage having an opening extending through the outer shell. The airflow passage may extend between the outer shell and the intermediate shell as well as between the intermediate shell and the inner shell. The airflow passage may provide fluid communication between the opening and the combustion chamber. The ignition device may be at least partially disposed within the housing assembly and may ignite fuel received from a fuel source and air received from the airflow passage to produce a flame in the combustion chamber. The airflow passage may be in a heat transfer relationship with the flame in the combustion chamber.

FIELD

The present disclosure relates to a system for treating exhaust gases.More particularly, an exhaust aftertreatment burner with preheatedcombustion air is discussed.

BACKGROUND

This section provides background information related to the presentdisclosure and is not necessarily prior art.

In an attempt to reduce the quantity of NO_(X) and particulate matteremitted to the atmosphere during internal combustion engine operation, anumber of exhaust aftertreatment devices have been developed. A need forexhaust aftertreatment systems particularly arises when dieselcombustion processes are implemented. Typical aftertreatment systems fordiesel engine exhaust may include one or more of a diesel particulatefilter (DPF), a selective catalytic reduction (SCR) system, ahydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC).

During engine operation, the DPF traps soot emitted by the engine andreduces the emission of particulate matter (PM). Over time, the DPFbecomes loaded and begins to clog. Periodic regeneration or oxidation ofthe trapped soot in the DPF is required for proper operation. Toregenerate the DPF, relatively high exhaust temperatures in combinationwith an ample amount of oxygen in the exhaust stream are needed tooxidize the soot trapped in the filter.

The DOC is typically used to generate heat to regenerate the soot loadedDPF. When hydrocarbons (HC) are sprayed over the DOC at or above aspecific light-off temperature, the HC will oxidize. This reaction ishighly exothermic and the exhaust gases are heated during light-off. Theheated exhaust gases are used to regenerate the DPF.

Under many engine operating conditions, however, the exhaust gas is nothot enough to achieve a DOC light-off temperature of approximately 300°C. As such, DPF regeneration does not passively occur. Furthermore,NO_(X) adsorbers and selective catalytic reduction systems typicallyrequire a minimum exhaust temperature to properly operate. Therefore, aburner may be provided to heat the exhaust stream upstream of thevarious aftertreatment devices to a suitable temperature to facilitateregeneration and efficient operation of the aftertreatment devices.While burners have been associated with exhaust treatment systems in thepast, it may be beneficial to provide an improved burner and mixersystem to provide improved ignition at very low temperatures, improvedheat transfer between the exhaust gas and the burner, improved fuelefficiency and/or energy usage, and robust longevity.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present disclosure provides a burner for an exhaustaftertreatment system. The burner may include a housing assembly and anignition device. The housing assembly may include an inner shellsurrounded by an intermediate shell and an outer shell. The inner shellmay at least partially define a combustion chamber. The housing assemblymay include an airflow passage having an opening extending through theouter shell. The airflow passage may extend between the outer shell andthe intermediate shell as well as between the intermediate shell and theinner shell. The airflow passage may provide fluid communication betweenthe opening and the combustion chamber. The ignition device may be atleast partially disposed within the housing assembly and may be operableto ignite fuel received from a fuel source and air received from theairflow passage to produce a flame in the combustion chamber. Theairflow passage may be in a heat transfer relationship with the flame inthe combustion chamber.

In another form, the present disclosure provides an exhaustaftertreatment system that may include an exhaust passage, an exhaustaftertreatment device, and a burner. The exhaust passage may receiveexhaust gas from an engine. The exhaust aftertreatment device may bedisposed in the exhaust passage. At least a portion of the burner may bein heat transfer relation with the exhaust gas flowing through theexhaust passage upstream of the exhaust aftertreatment device. Theburner may include a housing assembly having an inner shell surroundedby an intermediate shell and an outer shell. The inner shell may atleast partially define a combustion chamber. The housing assembly mayinclude an airflow passage having an opening extending through the outershell. The airflow passage may extend between the outer shell and theintermediate shell as well as between the intermediate shell and theinner shell. The airflow passage may provide fluid communication betweenthe opening and the combustion chamber. The airflow passage may be in aheat transfer relationship with a flame in the combustion chamber.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic representation of an engine and exhaustaftertreatment system according to the principles of the presentdisclosure;

FIG. 2 is a perspective view of a burner of the exhaust aftertreatmentsystem of FIG. 1;

FIG. 3 is an exploded perspective view of the burner;

FIG. 4 is a perspective cross-sectional view of the burner;

FIG. 5 is a cross-sectional view of the burner;

FIG. 6 is a perspective view of a nozzle assembly of the burner;

FIG. 7 is a cross-sectional view of the nozzle assembly taken along line7-7 of FIG. 6;

FIG. 8 is a cross-sectional view of the nozzle assembly taken along line8-8 of FIG. 6;

FIG. 9 is a cross-sectional view of the nozzle assembly taken along line9-9 of FIG. 6;

FIG. 10 is a flow chart illustrating operation of a flame sensor of theburner;

FIG. 11 is a cross-sectional view of the burner installed in a mixerhousing according to the principles of the present disclosure;

FIG. 12 is a perspective cross-sectional view of the burner and mixerhousing of FIG. 11; and

FIG. 13 is a side view of the mixer housing of FIG. 11.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

FIG. 1 depicts an exhaust gas aftertreatment system 10 for treating theexhaust output from an exemplary engine 12 to a main exhaust passageway14. An intake passage 16 is coupled to the engine 12 to providecombustion air thereto. A turbocharger 18 includes a driven member (notshown) positioned in an exhaust stream. During engine operation, theexhaust stream causes the driven member to rotate and provide compressedair to the intake passage 16 prior to entry into the engine 12. It willbe appreciated that the exhaust gas aftertreatment system 10 can also beused to treat exhaust output from a naturally aspirated engine or anyother engine that does not include a turbocharger.

The exhaust aftertreatment system 10 may include a burner 26 thatreceives and burns fuel from a fuel delivery system 98 and air from anair delivery system 110. The burner 26 is positioned downstream from theturbocharger 18 and upstream from a number of exhaust aftertreatmentdevices. The exhaust aftertreatment devices may include a hydrocarboninjector 28, a diesel oxidation catalyst 30 and/or a diesel particulatefilter 32, for example.

The burner 26 may be positioned in a heat transfer relationship withexhaust gas flowing through the main exhaust passageway 14. As shown inFIG. 1, the burner 26 may be at least partially disposed within a mixerhousing 400. The mixer housing 400 may be a part of or disposed in themain exhaust passageway 14 so that the exhaust gas may flow into themixer housing and around the burner 26 to transfer heat between theexhaust gas and the burner 26. The burner 26 may be used to heat theexhaust gas passing through the main exhaust passageway 14 to anelevated temperature that will enhance the efficiency of the DOC 30 andallow regeneration of the DPF 32. Additionally or alternatively, theburner 26 may be used prior to startup of the engine 12 to pre-heat theemissions system so that the effectiveness of the emissions system atengine startup is improved, thereby reducing cold-start emissions.

As shown in FIGS. 2-5, the burner 26 may include a housing assembly 40,a nozzle assembly 36, and a flame sensor assembly 37. The housingassembly 40 may be constructed as a multi-piece assembly of fabricatedmetal components. The housing assembly 40 may include an outer shell 42,an intermediate shell 44, and an inner shell 46. As shown in FIGS. 4 and5, the outer, intermediate and inner shells 42, 44, 46 may besubstantially concentric with each other such that the outer andintermediate shells 42, 44 may cooperate to define a first annularpassage 48 therebetween, and the intermediate and inner shells 44, 46may cooperate to define a second annular passage 50 therebetween. Thefirst and second annular passages 48, 50 may be in fluid communicationwith each other through one or more apertures 49 in the intermediateshell 44.

The shells 42, 44, 46 may include generally cylindrical tube portions51, 52, 54, respectively, and generally funnel-shaped backwall portions56, 58, 60, respectively. The first ends 62, 64, 66 of respective tubeportions 51, 52, 54 may be welded or otherwise attached to first ends68, 70, 72 of the backwall portions 56, 58, 60, respectively. The secondends 74, 78 of respective outer and inner tube portions 51, 54 may bewelded or otherwise attached to a second end 76 of the intermediate tubeportion 52. An inner surface 96 of the inner shell 46 may define acombustion chamber 94 (shown in FIGS. 4 and 5). A flame tube 95 may bedisposed within the combustion chamber 94 to act as a vaporizing elementby inducing recirculation of oxygen-poor combustion products within thecombustion chamber 94. The recirculation results in the completevaporization of the fuel and may cause the flame within the combustionchamber 94 to be a blue flame, which is indicative of a clean-burning,low-emissions flame. The flame tube 95 may be connected to the innersurface 96 by one or more brackets 92. A vaned diffuser 77 may beconnected to the housing assembly 40 at or proximate the second ends 74,76, 78 of the tube portions 51, 52, 54 and may diffuse and swirl heatedair exiting the burner 26.

Second ends 80, 82, 84 of the backwall portions 56, 58, 60 may fixedlysupport a nozzle bushing 86 that receives the nozzle assembly 36. Thenozzle bushing 86 may be slidably relative to the second ends 80, 82, 84to allow for thermal expansion and contraction of the intermediate andinner shells 44, 46 relative to each other and the outer shell 42. Thenozzle bushing 86 may be an annular member including a main aperture 87and a recessed portion 88. The recessed portion 88 may be disposedadjacent the combustion chamber 94 and may include a plurality ofradially extending apertures 90 in fluid communication with the secondannular passage 50. The nozzle assembly 36 is fixedly received in themain aperture 87. A portion of the nozzle assembly 36 may extend atleast partially through the recessed portion 88 proximate the combustionchamber 94.

The backwall portion 56 of the outer shell 42 may include an air inletport 119 that provides fluid communication between the air deliverysystem 110 and the first annular passage 48. During operation of theburner 26, air from the air delivery system 110 may flow in a serpentineflow path from the air inlet port 119, through the first and secondannular passages and into the combustion chamber 94, as shown in FIG. 4.That is, the air from the air delivery system 110 may flow into the airinlet port 119, then through the first annular passage 48. The air maythen flow through the apertures 49 into the second annular passage 50.The air may then flow through the annular passage 50 and into thecombustion chamber 94 through the apertures 90 in the nozzle bushing 86.In the combustion chamber 94, the air and fuel may be ignited. Afterignition, incoming air flowing through the first and second annularpassages 48, 50 may absorb heat from the outer, intermediate and innershells 42, 44, 46 and from flames in the combustion chamber 94 as theair flows through the serpentine flow path prior to combustion in thecombustion chamber 94. In this manner, the air can be preheated prior tocombustion and can cool the outer, intermediate and inner shells 42, 44,46. The nozzle assembly 36 may inject and ignite a mixture of fuelreceived from the fuel delivery system 98 and air received from the airdelivery system 110. The fuel may be a conventional diesel fuel or anyhydrocarbon-based or hydrogen-based fuel, for example. The nozzleassembly 36 may be structured as a combined injector that injects boththe fuel and air or separate injectors may be provided for the fuel andthe air.

As shown in FIGS. 6-9, the nozzle assembly 36 may include a main body120, an outer nozzle body 122, an inner nozzle body 123, a nozzle cap124 and a glow plug 126. The main body 120 includes a generallycylindrical member having an outer surface 128 and a radially extendingflange 130. The outer surface 128 may be received in the main aperture87 such that the flange 130 abuts an axial end 132 of the nozzle bushing86, as shown in FIGS. 4 and 5. A plurality of bolts 134 (FIGS. 2 and 3)may secure the flange 130 to the nozzle bushing 86. It will beappreciate that the main body 120 could be secured to the nozzle bushing86 by any other suitable means, such as welding or a press fit, forexample. In some embodiments, the main body 120 could be integrallyformed with the nozzle bushing 86.

As shown in FIGS. 7-9, the main body 120 may also include a first recess136, a central aperture 138 and a second recess 140. The glow plug 126may threadably engage the first recess 136 and may extend through thecentral aperture 138 and the second recess 140. The outer nozzle body122 may be fixedly received in the second recess 140. The inner nozzlebody 123 may be slidably received in the central aperture 138 to allowfor axial expansion and contraction of the inner nozzle body 123 toallow for axial thermal expansion and contraction of the inner nozzlebody 123.

The main body 120 may also include a fuel inlet passage 97 (shown inFIG. 8) and an air inlet passage 99 (shown in FIG. 9). The fuel inletpassage 97 may extend through an end 142 of the main body 120 to thefirst recess 136. The air inlet passage 99 may extend through the end142 of the main body 120 to the second recess 140.

As shown in FIG. 1, the fuel inlet passage 97 is in fluid communicationwith the fuel delivery system 98. The fuel delivery system 98 mayinclude a fuel tank 100, a fuel filter 102, and a fuel pump 104interconnected by a fuel line 108. In some embodiments, the fuel pump104 may be a metering-type pump whereby a pump motor speed is increasedor decreased to control the fuel delivery rate. The pump 104 may becontrolled based on feedback from the flame sensor assembly 37. In someembodiments, the fuel delivery system 98 could include a fuel block (notshown) controlling delivery of the fuel. The fuel line 108 may bedirectly or indirectly coupled with the fuel inlet passage 97. Operationof the components of the fuel delivery system 98 selectively providesfuel to the nozzle assembly 36. The air inlet passage 99 is in fluidcommunication with the air delivery system 110. The air delivery system110 may include a secondary air filter 112 and a MAF sensor 114. Acompressor 116 is in receipt of air that is passed through the secondaryair filter 112 and the MAF sensor 114. The compressor 116 may include aportion of a supercharger, the turbocharger 18 or a stand-alone electriccompressor. Output from the compressor 116 is provided to the air inletpassage 99 via an air supply line 118. The air supply line 118 alsosupplies air to the air inlet port 119 of the outer shell 42.

In some embodiments, a valve 117 may be disposed downstream of thecompressor 116 to control airflow into the nozzle assembly 36 and intothe inlet 119. The valve 117 may be configured to ensure a predeterminedamount of air flows into the nozzle assembly 36. For example, in someembodiments, the valve 117 may be configured so that air pressure at theinlet of the nozzle assembly 36 is about five pounds per square inch(psi) higher than air pressure at the inlet 119. It will be appreciated,however, that the majority of the air flowing through the air supplyline 118 may flow into the inlet 119 with a relatively small portionbeing diverted to the nozzle assembly 36 to atomize the fuel in thenozzle assembly 36.

Referring again to FIGS. 6-9, the outer nozzle body 122 may include acylindrical portion 144 and a frustoconical portion 146. The cylindricalportion 144 may be fixedly received in the second recess 140 of the mainbody 120 such that the frustoconical portion 146 abuts an end of themain body 120. The outer nozzle body 122 may be welded or otherwisefixed to the main body 120.

The outer nozzle body 122 may also include first and second recesses148, 150. The first recess 148 may be partially defined by an annularflange 152. The second recess 150 may extend from an axial end of thecylindrical portion 144 through a portion of the frustoconical portion146 and into the first recess 148. The second recess 150 may be definedby a cylindrical annular surface 153 and a tapered annular surface 154adjacent the first recess 148.

The inner nozzle body 123 may include a body portion 156, a and a headportion 158. The body portion 156 may extend from the first recess 136of the main body 120 through the central aperture 138 and through aportion of the second recess 140. The body portion 156 may include anouter surface 160 and an inner surface 162. The outer surface 160 mayinclude a cylindrical portion 164 and a tapered portion 166. Thecylindrical portion 164 may be received in the central aperture 138 by aslip fit, for example. The cylindrical portion 164 and the taperedportion 166 of the outer surface 160 may cooperate with the cylindricalannular surface 153 and the tapered annular surface 154, respectively,of the outer nozzle body 122 to define an annular passageway 168 influid communication with the air inlet passage 99. The inner surface 162of the body portion 156 of the inner nozzle body 123 may define agenerally cylindrical interior cavity 170 having a tapered end 172. Theinterior cavity 170 may be in fluid communication with the fuel inletpassage 97 via the first recess 136.

The head portion 158 of the inner nozzle body 123 may extend radiallyoutward from an end of the tapered portion 166 of the body portion 156.The nozzle cap 124 and head portion 158 may be received in the firstrecess 148 of the outer nozzle body 122. The nozzle cap 124 may bewelded to the outer nozzle body 122, thereby securing the head portion158 within the first recess 148. The head portion 158 may include a fueldischarge aperture 174 and a plurality of air discharge apertures 176.The fuel discharge aperture 174 may be in fluid communication with theinterior cavity 170 and an exit aperture 178 of the nozzle cap 124. Theair discharge apertures 176 may be in fluid communication with theannular passageway 168 and the exit aperture 178 of the nozzle cap 124.Fuel discharged from the fuel discharge aperture 174 may be atomized inthe exit aperture 178 and/or downstream of the exit aperture 178 by thehigh-pressure air discharged from the air discharge apertures 176.

The glow plug 126 may include a bushing portion 180 and a heater rod182. The glow plug 126 can be a 120 W Kyocera SiN glow plug, forexample, or any other suitable glow plug or other heating element. Thebushing portion 180 may be threadably received in the first recess 136of the main body 120. The heater rod 182 may extend from the bushingportion 180 into the interior cavity 170. The heater rod 182 and theinterior cavity 170 may be sized such that an annular space 184 existsbetween the heater rod 182 and the inner surface 162 of the body portion156 of the inner nozzle body 123.

While the nozzle assembly 36 is described above as including anintegrated glow plug, additionally or alternatively, a spark plug orother ignition device could be provided for igniting the fuel and air.The spark plug or other ignition device could be separate and distinctfrom the nozzle assembly 36 or integrated therein.

A control module 38 (FIG. 1) is provided to monitor and control theflows of fuel and air through the nozzle assembly 36 and monitor andcontrol operation of the glow plug 126 using any suitable processor(s),sensors, flow control valves, electric coils, etc. The control module 38may include or be part of an Application Specific Integrated Circuit(ASIC), an electronic circuit, a processor (shared, dedicated or group)and/or memory (shared, dedicated or group) that execute one or moresoftware or firmware programs, a combinational logic circuit and/orother suitable components that provide the described functionality. Thecontrol module 38 may be a part of or include a control unit controllingone or more other vehicle systems. Alternatively, the control module 38may be a control unit dedicated to the exhaust aftertreatment system 10.

The control module 38 may operate the glow plug 126 in one of aplurality of operational modes to serve specific purposes. For example,the control module 38 may operate the glow plug 126 at a high powerlevel to heat the fuel in the inner nozzle body 123 to a temperaturebeyond the fuel's auto-ignition point so that when the fuel comes intocontact with pressurized air in the exit aperture 178 and/or in thecombustion chamber 94, the fuel will spontaneously ignite. Once theburner 26 is lit, the control module 38 may discontinue or reduce theelectrical power to the glow plug 126 to reduce the temperature of theglow plug 126 to a point at which the glow plug 126 preheats the fuel toallow for passive vaporization of the fuel in the flame tube 95.

Periodically and/or at the end of a burn cycle (i.e., when the controlmodule 38 determines that the aftertreatment devices have beenadequately heated to a point at which the burner 26 need not be operatedto heat up the aftertreatment devices), the glow plug 126 may beoperated in a cleaning mode or decoking mode. In the cleaning mode ordecoking mode, the supply of fuel to the nozzle assembly 36 may be shutoff and the glow plug temperature may be increased to burn off anyvarnish and/or carbon deposits that may have accumulated on the nozzleassembly 36. After this cleaning cycle is complete, the glow plug 126may be powered down to a low level and the temperature of the glow plug126 may be monitored (it will be appreciated that the temperature of theglow plug 126 may be monitored at any time during operation of the glowplug 126). Monitoring of the glow plug temperature may be accomplishedby way of a calculation based on the resistance of the glow plug 126,which can be determined based on the voltage and current supplied to theglow plug 126. In some embodiments, air may continue to be pumpedthrough the nozzle assembly 36 during the cleaning and/or monitoringcycles to prevent soot and/or other debris from entering the nozzleassembly 36 from the combustion chamber 94.

Monitoring of the temperature of the glow plug 126 based on the glowplug resistance can be carried out during any or all of the operationalmodes described above. The control module 38 may adjust a power level(e.g., a pulse width modulation duty cycle) of the glow plug 126 basedon the temperature of the glow plug 126. In this manner, the controlmodule 38 may supply no more electrical power than is necessary toachieve a particular purpose. Monitoring the glow plug temperature andadjusting the power level accordingly can also ensure that the glow plug126 is not heated beyond its rated temperature threshold, nor subjectedto thermal shock due to heating and/or cooling faster than a thresholdrate, thereby preventing damage to the glow plug 126 due to overheating.

Referring now to FIGS. 1 and 5, the flame sensor assembly 37 may besupported by the backwall portions 56, 58, 60 of the housing assembly40. The flame sensor assembly 37 may include a bushing 190, a flame rod192, an insulator 193, and a heating element 194 (shown schematically inFIG. 5). The bushing 190 may engage one or more of the backwall portions56, 58, 60 and may receive the flame rod 192 and insulator 193. Theinsulator 193 may be a tube formed from Alumina and may surround aportion of the flame rod 192. The heating element 194 may be embedded inthe insulator 193 at a location proximate the backwall 60 (i.e., at theentry point to the combustion chamber 94). The insulator 193 may passthrough and slidably engage the backwalls 58, 60, and clearance may bemanaged to reduce leakage of air therebetween.

The flame rod 192 may be an elongated high-temperature wire including anelectrode 196 that may be positioned at least partially within orproximate the combustion chamber 94. A bias voltage may be applied tothe flame sensor 192 to create an electric field from the electrode 196to a ground such as the inner shell 46. When voltage is applied, anelectric field may radiate from the electrode 196 to the ground. If freeions are present in the field, an ion current may flow. The magnitude ofthe ion current provides an indication of the density of the ions. Thecontrol module 38 detects and receives signals from the flame sensorassembly 37 indicative of the ion current to determine the presence orabsence of a flame within the combustion chamber 94. The sensor assembly37 may also determine if the insulator 193 is fouled. While the flamesensor 192 is described above as being an ion sensor, it will beappreciated that, in some embodiments, the flame sensor 192 couldinclude any other type of flame sensor such as an optical sensor or athermocouple, for example.

The heating element 194 of the sensor assembly 37 may be include aresistance heater embedded in the insulator, for example, or anysuitable electrical resistance heating device. The heating element 194is in conductive heat transfer relation with the insulator 193 and maybe coaxial with the electrode 196. The insulator 193 may electricallyisolate the heating element 194 from the electrode 196 and any metalliccomponents of the housing assembly 40 and may act as a heat-resistantstructural support. The heating element 194 may be at least partiallydisposed in the combustion chamber 94. In an exemplary embodiment, theheating element 194 may span at least about 10 mm in length and may bedisposed about 20 mm from a distal tip of the electrode 196.

As will be subsequently described, the heating element 194 may beoperable in a cleaning or decoking mode and in a monitoring mode. In thedecoking mode, the control module 38 may cause electrical current to beapplied to the heating element 194 to burn off any deposits and/orcontamination that may accumulate on the insulator 193 due to exposureto exhaust gases and/or combustion in the combustion chamber 94. In themonitoring mode, the control module 38 may apply a reduced electricalcurrent to the heating element 194 and determine a resistance of theheating element 194 based on the voltage and current applied to theheating element 194. From the resistance, the temperature of the heatingelement 194 can be calculated or determined from a lookup table. In thismanner, the control module 38 can use the heating element 194 as acombustion chamber temperature sensor. That is, the temperature of theheating element 194 indicates the temperature of the combustion chamber94. The control module 38 may compare temperature data acquired from theheating element 194 with data from the flame sensor 192. If the datafrom the heating element 194 indicates the presence of a flame in thecombustion chamber 94 and the flame sensor 192 does not indicate thepresence of a flame, the control module 38 may operate the burner 26 ina reduced capacity mode or a “limp mode” rather than completelydisabling the burner 26.

Fouling of the insulator 193 may occur through deposition of soot, oiland/or other contaminants that form a conductive bridge from the flamerod 196 to ground where the insulator passes through the backwall 60.When the insulator 193 is fouled, it may not be possible todifferentiate between ion current flow through a flame and leakagecurrent to ground through the conductive contaminants. Therefore, thecontrol module 38 may determine whether the insulator 193 issufficiently clean to allow the flame sensor assembly 37 to functioncorrectly prior to ignition of the burner 26. If the flame sensorassembly 37 is determined to be ready for operation, the control module38 may ignite the burner 26.

The control module 38 may evaluate a number of other parametersincluding presence of combustion and temperature of the exhaust gaswithin the main exhaust passageway 14 at a location downstream from theburner 26 to determine when to cease the supply of fuel and air to theburner 26. For example, the control module 38 may receive signals fromone or more temperature sensors located within the burner 26 or withinthe main exhaust passageway 14 to perform a closed loop control byoperating the burner 26 to maintain a desired temperature at aparticular location. If combustion unexpectedly extinguishes, thecontrol module 38 may cease the supply of fuel and/or attempt to relightthe burner 26. Other control schemes are also within the scope of thepresent disclosure.

With reference to FIG. 10, a method of operating the sensor assembly 37will be described in detail. At step 210, prior to ignition of theburner 26, the control module 38 may cause a bias voltage to be appliedto the flame sensor 192. At step 220, a resulting current flow throughthe flame sensor 192 may be determined. At step 230, the control module38 may determine whether the current flow through the flame sensor 192(determined at step 220) is less than or greater than a predeterminedvalue. Any appreciable current flow through the flame sensor 192 when aflame is not present in the combustion chamber 94 indicates that sootand/or other contaminants have accumulated on the insulator 193 and thedetected current flow is a leakage current flow through contamination onthe insulator 193. Therefore, the predetermined value may be a verysmall value or any value that indicates an amount of contamination onthe insulator 193 that could affect the performance of the flame sensor192.

If the control module 38 determines that the current flow through theflame sensor 192 is greater than the predetermined value at step 230,the control module 38 may cause the heating element 194 to operate inthe decoking mode at step 240. In the decoking mode, electrical powermay be applied to the heating element 194 by pulse-width modulation, forexample, to raise the heating element 194 to a temperature (e.g., about650 degrees Celsius or more) that will burn soot deposits and/or othercontamination off of the insulator 193. The control module 38 may varythe duty cycle of the pulse-width modulated power to the heating element194 to control the temperature of the heating element 194. Thetemperature of the heating element 194 may be determined by firstcalculating the resistance of the heating element 194 based on a knownvoltage and detected current flow therethrough. The temperature of theheating element 194 can then be determined based on the resistance byway of a calculation or a lookup table, for example.

During operation of the heating element 194 in the decoking mode, thecontrol module 38 may continue to monitor the current flowing throughthe flame sensor 192, as described above with respect to steps 210-230.As the soot and/or other contaminants are burned off of the insulator193, the current through the flame sensor 192 may drop off to anacceptable level. Once the current flow has reached an acceptable level,the control module 38 may cause the heating element 194 to operate inthe monitor mode at step 250.

In the monitor mode, the control module 38 may cause a reduced dutycycle to be applied to the heating element 194. The duty cycle appliedto the heating element 194 in the monitor mode may be any duty cyclethat allows calculation of the electrical resistance of the heatingelement 194 so that the temperature of the heating element 194 can bemonitored. In this manner, the heating element 194 may provide feedbackto the control module 38 indicating the temperature of the combustionchamber 94 and whether a flame is present in the combustion chamber 94.In some embodiments, no more current is provided to the heating element194 in the monitor mode than is necessary to calculate the resistance ofthe heating element 194.

At step 255, the control module 38 may determine whether conditions aresuch that the burner 26 should be operated to heat exhaust gas in themain exhaust passageway 14 and/or one or more of the aftertreatmentdevices. If the control module 38 determines that the burner 26 shouldbe operated, the control module 38 may, at step 260, operate the burner26 and continue to operate the flame sensor assembly 37. That is, fueland air may be supplied to the burner 26 and ignited therein, andvoltage may be applied to the flame sensor 192. At step 270, the controlmodule 38 may determine the ion current flow through the flame sensor192 as a result of the bias voltage applied thereto. At step 280, thecontrol module 38 may determine whether the ion current flow through theflame sensor 192 indicates the presence of a flame in the combustionchamber 94. If data from the flame sensor 192 indicates that a flame ispresent in the combustion chamber 94, the control module 38 maydetermine, at step 290, whether temperature data received from theheating element 194 (during operation of the heating element 194 in themonitor mode) also indicates the presence of a flame in the combustionchamber 94. If temperature data from the heating element 194 alsoindicates the presence of a flame in the combustion chamber 94,operation of the burner 26 may continue, as necessary. If temperaturedata from the heating element 194 indicates a lack of a flame in thecombustion chamber 94, the control module 38 may operate the burner 26in a reduced capacity mode or a limp mode at step 300. The controlmodule 38 may also generate an error signal that may alert the driver ofthe vehicle that a fault has been detected in the aftertreatment system10 and that service of the aftertreatment system 10 may be necessary.

If, at step 280, data from the flame sensor 192 indicates that a flameis not present in the combustion chamber 94, the control module 38 maydetermine, at step 310, whether temperature data received from theheating element 194 also indicates the lack of a flame in the combustionchamber 94. If temperature data from the heating element 194 alsoindicates the lack of a flame in the combustion chamber 94, the controlmodule 38 may shutdown the burner 26 (i.e., discontinue the supply offuel and air to the burner 26) at step 320. If temperature data from theheating element 194 indicates the presence of a flame in the combustionchamber 94, the control module 38 may operate the burner 26 in a reducedcapacity mode or a limp mode at step 300 and generate an error signalalerting the driver that a fault has been detected in the aftertreatmentsystem 10.

It will be appreciated that the response-time of the heating element 194to changes in temperature may be slower than the response-time of theflame sensor 192. Therefore, the control module 38 may account for thelagging response-time of the heating element 194 when determining (atsteps 290 and 310) whether temperature data from the heating element 194indicates the presence or lack of a flame in the combustion chamber 94.

With reference to FIGS. 1 and 11-13, the mixer housing 400 will bedescribed in detail. The mixer housing 400 may support the burner 26relative to the main exhaust passageway 14 and may fluidly coupleupstream and downstream portions 401, 403 (FIGS. 1 and 11) of the mainexhaust passageway 14. The mixer housing 400 may include a main body402, an inlet body 404, a first vaned diffuser 406 and a second vaneddiffuser 408.

The main body 402 may include a tubular shell 410 and an annularbackwall 412. The tubular shell 410 may include first and second axialends 414, 416 and an inlet opening 418 disposed between the first andsecond axial ends 414, 416. The backwall 412 may be fixedly attached toor integrally formed with the tubular shell 410 at the first axial end414. The first diffuser 406 may be disposed within the tubular shell 410and may be fixed relative thereto between the inlet opening 418 and thesecond axial end 416. The second diffuser 408 may be fixedly attached tothe tubular shell 410 at or proximate the second axial end 414. In thismanner, the mixer housing 400 may define a first chamber 420 within thetubular shell 410 between the backwall 412 and the first diffuser 406and a second chamber 422 within the tubular shell 410 between the firstand second diffusers 406, 408. The second axial end 414 and the seconddiffuser 408 may define an outlet of the second chamber 422 that isfluidly coupled with the downstream portion 403 of the main exhaustpassageway 14.

The first diffuser 406 and the backwall 412 may both be annular membersincluding central openings 424, 426, respectively. The burner 26 mayextend through the openings 424, 426 and the outer shell 42 of theburner 26 may fixedly engage the backwall 412 and the first diffuser406. In this manner, at least a portion of the housing assembly 40 ofthe burner 26 may be received in the first chamber 420. The tubeportions 51, 52, 54 of the housing assembly 40 of the burner 26 may besubstantially concentric with the tubular shell 410 of the mixer housing400 (i.e., the tube portions 51, 52, 54 may share a common longitudinalaxis Al with the tubular shell 410). It will be appreciated, however,that in some embodiments, the tube portions 51, 52, 54 may be eccentricrelative to the tubular shell 410.

The second ends 74, 76, 78 of the tube portions 51, 52, 54 of thehousing assembly 40 may extend into the second chamber 422 such thatheated air and combustion gas may exit the burner 26 through itsdiffuser 77 and flow into the second chamber 422 where the heated airand combustion gas may mix with exhaust gas from the main exhaustpassageway 14. The mixture of exhaust gas and heated gas from the burner26 may exit the mixer housing 400 through the second diffuser 408 andflow into the downstream portion 403 of the main exhaust passageway 14.

The inlet body 404 may be a tubular member including a longitudinal axisA2, a first axial end 430 and a second axial end 432. The first axialend 430 may be fluidly coupled with the upstream portion 401 of the mainexhaust passageway 14. The second axial end 432 may be fluidly coupledwith the inlet opening 418 of the main body 402. In this manner, theinlet body 404 feeds exhaust gas from the upstream portion 401 of themain exhaust passageway 14 into the first chamber 420 of the mixerhousing 400.

The inlet body 404 may be positioned relative to the main body 402 suchthat the longitudinal axis A2 of the inlet body 404 may be substantiallyperpendicular to the longitudinal axis A1 of the tubular shell 410 (asshown in FIGS. 11 and 13) and offset from the longitudinal axis A1 sothat the longitudinal axes A1, A2 do not intersect each other (as shownin FIG. 13). In other embodiments, the axis A2 may be parallel to andintersect the axis A1 (i.e., the inlet body 404 may extend radially fromthe main body 402).

The offset position of the inlet body 404 relative to the main body 402shown in FIG. 13 (i.e., the offset position of the axis A2 relative tothe axis A1) may allow at least a portion of the exhaust gas to enterthe first chamber 420 generally tangentially. This tangential flow intothe first chamber 420 may induce a swirled flow within the first chamber420 and may facilitate a more uniform flow of the exhaust gas throughthe annular space around the housing assembly 40, thereby improving thetransfer of heat from the exterior surfaces of the housing assembly 40to the exhaust gas. The exhaust gas in the first chamber 420 may befluidly isolated from the air and combustion gas within the burner 26until the exhaust gas and the air and combustion gas from the burner 26are combined in the second chamber 422.

From the first chamber 420, the exhaust gas may flow through the firstdiffuser 406 and into the second chamber 422. Vanes 407 of the firstdiffuser 406 may further induce swirling of the exhaust gas passingtherethrough. The vanes 75 of diffuser 77 of the burner 26 may induceswirling of the heated air and combustion gas exiting the burner 26. Theswirling flow of exhaust gas, heated air and combustion gas within thesecond chamber 422 may facilitate mixing of the exhaust gas with theheated air and combustion gas and facilitate heating of the exhaust gasin the second chamber 422. The vanes 409 of the second diffuser 408 mayfurther induce swirling of the mixture of the exhaust gas and heated airand combustion gas as it exits the second chamber 422 and flows into thedownstream portion 403 of the main exhaust passageway 14. In thismanner, the exhaust gas in the downstream portion 403 of the mainexhaust passageway 14 may be sufficiently heated prior to interactionwith the aftertreatment devices 28, 30, 32 (FIG. 1).

In some embodiments, the vanes 75, 407, 409 of the diffusers 77, 406,408 may all be angled or oriented in the same direction so that thediffusers 77, 406, 408 all generate a swirling effect in the samerotational direction. In other embodiments, one of the sets of vanes 75,407, 409 may be angled or oriented in the opposite direction so that oneof the diffusers 77, 406, 408 generates a swirling effect in an oppositerotational direction relative to the rotational directions of theswirling effects of the other two diffusers 77, 406, 408.

In some embodiments, the main body 402 may include an insulation member440 (FIG. 11) that lines the inner diameter of the tubular shell 410 inthe second chamber 422. The insulation member 440 may include an annularshell 442 encasing a fibrous insulation material 444, for example, andmay reduce heat loss from the second chamber 422 (i.e., reduce thetransfer of heat from the second chamber 422 to the ambientenvironment). This improves the efficiency of the mixer housing 400 andburner 26 and also maintains the outer surface of the tubular shell 410at a relatively moderate temperature.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A burner for an exhaust aftertreatment systemcomprising: a housing assembly including an inner shell surrounded by anintermediate shell and an outer shell, the inner shell at leastpartially defining a combustion chamber, the housing assembly includingan airflow passage having an opening extending through the outer shell,the airflow passage extending between the outer shell and theintermediate shell as well as between the intermediate shell and theinner shell, the airflow passage providing fluid communication betweenthe opening and the combustion chamber, the airflow passage including aserpentine flow path flowing between first and second axial ends of thehousing assembly in a first direction and between the first and secondaxial ends in a second direction; and an ignition device at leastpartially disposed within the housing assembly and operable to ignitefuel received from a fuel source and air received from the airflowpassage to produce a flame in the combustion chamber, the airflowpassage being in a heat transfer relationship with the flame in thecombustion chamber, wherein the outer, intermediate and inner shellsinclude outer, intermediate and inner tubular members, respectively,arranged concentrically with each other, the inner tubular member atleast partially defining the combustion chamber, the outer andintermediate tubular members surrounding the inner tubular member, thehousing assembly including outer, intermediate and inner backwalls eachformed separately from and attached to the outer, intermediate and innertubular members, respectively, and wherein the airflow passage includesa first annular passage disposed between the outer and intermediatetubular members and a second annular passage disposed between theintermediate and inner tubular members, the first annular passagesurrounding the second annular passage.
 2. The burner of claim 1,wherein the intermediate tubular member includes at least one apertureproviding fluid communication between the first and second annularpassages.
 3. The burner of claim 1, wherein the first annular passageextends between the outer and intermediate backwalls, and the secondannular passages extends between the intermediate and inner backwalls.4. The burner of claim 1, wherein the opening extends through the outerbackwall and provides fluid communication between an air supply line andthe first annular passage.
 5. The burner of claim 1, further comprisinga bushing supported by the outer, intermediate and inner backwalls andincluding a plurality of apertures providing fluid communication betweenthe second annular passage and the combustion chamber.
 6. The burner ofclaim 1, wherein a control module is in communication with the ignitiondevice and operable to control a supply of fuel and air to the burner.7. The burner of claim 6, further comprising an ion sensor incommunication with the control module and positioned at least partiallywithin the housing assembly to detect the presence of a flame in thecombustion chamber.
 8. The burner of claim 1, wherein the ignitiondevice includes at least one of a glow plug, a spark plug and a nozzle.9. An exhaust aftertreatment system comprising: an exhaust passagereceiving exhaust gas from an engine; an exhaust aftertreatment devicedisposed in the exhaust passage; and a burner in heat transfer relationwith the exhaust gas flowing through the exhaust passage upstream of theexhaust aftertreatment device, the burner including a housing assembly,the housing assembly including an inner shell surrounded by anintermediate shell and an outer shell, the inner shell at leastpartially defining a combustion chamber, the housing assembly includingan airflow passage having an opening extending through the outer shell,the airflow passage extending between the outer shell and theintermediate shell as well as between the intermediate shell and theinner shell, the airflow passage providing fluid communication betweenthe opening and the combustion chamber, the airflow passage being in aheat transfer relationship with a flame in the combustion chamber, theairflow passage including a serpentine flow path flowing between firstand second axial ends of the housing assembly in a first direction andbetween the first and second axial ends in a second direction, whereinthe outer, intermediate and inner shells include outer, intermediate andinner tubular members, respectively, arranged concentrically with eachother, the inner tubular member at least partially defining thecombustion chamber, the outer and intermediate tubular memberssurrounding the inner tubular member, the housing assembly includingouter, intermediate and inner backwalls each formed separately from andattached to the outer, intermediate and inner tubular members,respectively, and wherein the airflow passage includes a first annularpassage disposed between the outer and intermediate tubular members anda second annular passage disposed between the intermediate and innertubular members, the first annular passage surrounding the secondannular passage.
 10. The exhaust aftertreatment system of claim 9,wherein the intermediate tubular member includes at least one apertureproviding fluid communication between the first and second annularpassages.
 11. The burner of claim 9, wherein the first annular passageextends between the outer and intermediate backwalls, and the secondannular passages extends between the intermediate and inner backwalls.12. The exhaust aftertreatment system of claim 9, wherein the openingextends through the outer backwall and provides fluid communicationbetween an air supply line and the first annular passage.
 13. Theexhaust aftertreatment system of claim 9, wherein the burner includes abushing supported by the outer, intermediate and inner backwalls, thebushing including a plurality of apertures providing fluid communicationbetween the second annular passage and the combustion chamber.
 14. Theexhaust aftertreatment system of claim 9, further comprising a controlmodule in communication with an ignition device of the burner, thecontrol module is operable to control a supply of fuel and air to theburner.
 15. The exhaust aftertreatment system of claim 14, wherein theburner includes an ion sensor in communication with the control moduleand positioned at least partially within the housing assembly to detectthe presence of a flame in the combustion chamber.
 16. The exhaustaftertreatment system of claim 9, wherein the aftertreatment deviceincludes one or more of a hydrocarbon injector, a diesel oxidationcatalyst and a diesel particulate filter.